Abstract: The purpose of our study is to investigate the role of neurotransmitters, serotonin (5HT), dopamine (DA) and norepinephrine (NE) in the progression and pathogenesis of Alzheimer's disease (AD) and Alzheimer's Dementia Related Diseases (ADRD). Our study is one of the very few focusing on the brainstem neurotransmitter dysfunction defining neurodegenerative disease pathology as polygenic modulation of 5HT, DA and NE. Brainstem is very important area of the brain to assess neurodegeneration and treatment strategies in AD & ADRD and beyond. We are proposing to establish multidimensional biomarkers defining neurodegenerative diseases (NDDs), brain metabolic syndrome (bMets) and depression (NPS) and dissecting AD & ADRD molecular blue prints. Serotonin is important neurotransmitter to define and reverse neurodegenerative pathology in AD, ADRD and beyond i.e., probable reversal of mild cognitive impairment (MCI), cerebral strokes, and traumatic brain injury (TBI) pathologies. Small populations of neurons in hindbrain area characterized to express 5HT further define important pathological significance in NDDs and NPSs. Molecular links among 5HT, DA and NE in the brainstem are not completely understood and further how mRNA levels and microRNAs altered from non-demented state to MCI state, and MCI state to early AD state are unclear. In addition, we still do not know cellular changes that occur from non-demented healthy state to Lowy-body dementia (LBD), TBI, Fronto-temporal dementia (FTD) and depressed individuals with no dementia Therefore, in the current study, we propose to investigate mRNA levels and microRNAs using brainstem tissues ? raphe, locus coeruleus and substantia nigra from all 8 groups of tissues mentioned above. To achieve our objective, we use 2 Specific Aims: In Aim 1, we will investigate three important areas of the brain, including rostral to caudal substantia nigra, raphe and locus coeruleus to investigate neurotransmitters (DA/5HT/NE) mRNA expression in healthy subjects, depressed patients, MCI, TBI, LBD, TBI, AD Braak I/II and AD Braak V/VI. Samples from 3 target areas will be hybridized to Clariom D human pico chip and analyze for multiple pathways altered in different diseases. In Aim 2, we will validate differentially expressed mRNA and microRNA data in 8 groups analyzed in Aim 1. Further, using serum samples from all 8 groups and ELISA, we will assess protein levels of differentially expressed mRNAs and microRNAs from Aim 1. The outcome of our study will provide hypothesis generating gene expression and microRNA data, and this new information can be used for long-term R01 grants.